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E90/E91/E92/E93 (2006 - 2013) The E9X is the 4th evolution of the BMW 3 series including a highly tuned twin turbo 335i variant pushing out 300hp and 300 ft. lbs. of torque. BMW continues to show that it sets the bar for true driving performance! -- View the E9X Wiki

I had a gas cap left off and noticed the check engine light was on. I went out and sure enough saw the cap and put it on. That was three months ago, multiple fill ups since etc. But check engine remained on. Just had the code checked when doing an oil change and read a code 20. Also was reset. I have been on the forum and find much great info but can't tell if this was still triggered by that cap and just never went out of if it is 02 sensor (catalytic convertor related etc.). Can you help.....any ideas would be more than welcome. Thank you!!!